During a 1 h 30 min study session, a student uses three appliances as follows:
• A 500 W heater operates for the first 30 min only.
• A 150 W fan operates for the last 1 h only.
• A 100 W lamp stays on for the entire session.
The total electrical energy consumed in this period is closest to
(a) 0.50kWh
(b) 0.55kWh
(c) 0.45kWh
(d) 0.60kWh